I'd suggest the following two phrasings:

• I place terminal value to retribution (inflicting suffering on the causers of suffering), at least for some of the most egregious cases.
• I do not place terminal value to retribution, not even for the most egregious cases (e.g. mass murderers). I acknowledge that sometimes it may have instrumental value.

Perhaps also add a third choice:

• I think I place terminal value to retribution, but I would prefer it if I could self-modify so that I wouldn't.